Telephone system



y R. c. MATHEs 7 "2,006,470

TELEPHONE SYSTEM Filed'Sept. 9, 1932 oN HRMQ QEHFH a H .Eq o m MQI A? as t NW N at N\ a m u w $3 HT -H HHMU mm: .1. E1 NEG d 9 9 w k IN VE/V T 0/? R. C. AM THE 5 ATTORNEY Patented'Jul 2.11935 f we W I present inventionLrielates of waves'iorsignaling purposes; and particularly H to transmission'over two-wire; circuits on a, fourwire basis by use of idifierent-sfrequency ranges xii -the twoggdirectionsm The: use of; modulated-carrienwaves vfor-trans- .mission, over toll lines,;, in -which=..difierent Jfre+ I quency bands are used inxopposite': directionsis rfcommon.-;- lghe present invention. .iswmore a especially; concerned withzsecuring so-called equiv;

e alent four-wire transmission in the local plant, I that is. on-subscribersflflines.and'ptrunkcircuits; 3 Such transmissiongis 1 effected,: win ,accorda nce with thel: present invention; with a-simplified *apT- paratus byatransmitting at speech frequencyv =.i'n

one direction-- (specifically. from the -.s'ubstation) and atcarriertfrequency in the'opposite "direction 5 i(toward 'the'substation); Thisrequiresnospecial 'modulatin gapparatus at the substations? :A' sim-i .pletype demodulator such as-a copper oxide type maysbe used atethe substations: -am1:modulators and sources of carrier current are located at centraliofiicesfso thatthe unmodulatedf-carrier does not" need to be sent=to the-substations Q-io'r 'mOdu' lating purposes.

' A betterunderstanding ioi the irivention may be .gainedufrom the following description in cone}- ne'ction withithe drawing; 1- i r 1 .In Fig; 1 there-is" showna schematic dlagram of. a complete connect n between two? subscribersfiistatio'ns; Fig-z 2 "shows a simpli-fiejd type of cord circuit capable of use with th'specially'equippedifsubsets of the invention a'swellas withthe ordinanysubfsets; and I w 1 Flg.:3 shows the manner physical four-wire toll line. v

.In Fig, 1,.subscribers lines I and 2 lead from central oflice 3 to subscribers stationsjl and 5.

comprises an ordinary transmitter 6; our ordinary receiver 1, a detector 8, which may beaflc'opper oxide rectifier of simple type, a low'pass filter .8

and ahigh passfilter III. I

At central oflice 3, there is shown a cord circuit for interconnecting subsets 4 and}, consisting of filters 9 and III of the same type as the corresponding. filters at the substation, modulatorsv I l and a source of carrier waves I 2. Amplifiers, such as l3, will be provided wherever needed.

It will be understoodthat carrier source i2 is common to the exchange and may be an oscillator or machine generator wired to. all of the cord circuits. The cord circuit shown may be used to connect any pair of subscribers lines oithe types "aiihu'taiiil sep miier e. m suse;amt

- manner.

' iull {coupling efliciency and receivergrespectively and the 111i "H may, be copper+oxid jor dther isimple 'ype' for In local connections 0t connection to a The subscribers stations are both alike-and each,

Incorporated,

showm' Filtersaand l0 mayicom'prise the neces-' sary number; 10f. sections or filter {network :compris'ing inductance and=capacity "te -give the-irequired frequency 1 discri'mination between I the ranges utilized in the opposite -.directions or: trans missions, The-cord circuit may beprovided with repeating coil on each side and :me usual cen 1 u tral; oilicefbattery for 'supplying operatingburrent 1 1- to the microphones atethe.substations" ,JE When the subscriber aflstatiozil alks his may-have a pass rangebf=$5b0ftol5fi0 cycles: speech'from line: I arriving at the central-statics passes 1 through filte'r 8 w-moau e em :c wnere 'it combines withfthe carrler wav e now-source l 2 :toiproduce 'a' "carrier and' s'ideband in th'e pass range of filter III so that th" resulting waves go i out "over line 2 i "to station iiwhere they e 'ter "or being heard in receiverlt Waves' in the o'ppos'ite' directionfrom s'tation5 3 to station 4 rerransmitted menufly analogous.

Filters 9 and ill at n uescriiirfs stiapn and the other-apparatus"thereat are designed to give the respective filter passranges 'The they may: comprise space dl scharge devices latter cord circuits passing thecurr Without r quency translation."

The equivalent four-wire transmission such as is described above and illustrated in -1 ig'. 1 may 1 be extended to toll circuits. While its is mainly concerned with the localplant,"it is not,

therefore, to be consideredas limited to local plant. For example; in toll circuits generally considered too short to be operated on physical four-wire basis, equivalent Iour-wirezoperation may be secured by the method of the invention.

In Fig. 2 the usual central ofiice battery I! and cord circuit repeating coil ii are shown, but the latter-is provided withan extra winding H which is connected to the'junction' of filters 9 and I0 in'thecir'cuit of modulator ll.

Whenthe cord circuit of Fig. 2 is used to;inter-.

c ahis tween-"t e trai siiutgei if connect two ordinary subsets, the speech'isre- 5 peated by coil IS in .the usual manner. Speech currents are also sent into the input of the modulator ll via winding l1 and illter 9, and as a result a high frequency side band is produced and reapplied ;t the cord circuit through filter in and windingglli'uin the case or ordinary sub sets, however, this action has no effectexceptto reduce the efliciency of transmission to a certain,

extent.

Whenthe cord circuit is connected to a subset of the type shown in Fig. 1, however, these side.

a band currents along withsome carrierfa'refre ceived as in the case of -The,voi tieitfequency waves sent through the repeating coil it direct are, in that case,oi no=eflect. Thusthe cord circuit of Fig. 2 may be used during a change-over period while ordinary types or sub-i, stations and/substations in accordancewlth-this inventionl are bothjpresent inthevsystem. 1

inthe" output ofithecord circuit oi Fig..- 1. 1s to be applied, to a physical four-wire toll circuit, the connecting circuit-o! Fig. 3 may be In i this figure the'centralvoflice iswshown' atrluconnected by trunk;v -I 95 with wthe tour-wira circuit comprising ,transmitting, branch 20 and; receive ing branchILmI-Iigh pass; filter," and detector I translate the carrier frequency side bandto the, voice trequency level" for. transmission over line to the ordinary voice-frequency apparatus at the;distant endi y Inthe ireturn circuit 2 lyfllter 9 allows vthereceived.,speech waves to; be sent over, circuits" Eto' the; oflice .3, but prevents, the

1, point 22.

high:- ireduency .oppo sitely directed wavesqirom entering-circuit ll, ,In the case n! ordinary. twowire ;to tour-wire;connections, balance; and; echo difllculties; sometimes make it advantageous to periorm- 1 switchmg operations in the four-wire 20,4], dimcultiesare social; removed by the equivalentiour-wire operation of thednyentlon, however, as to enable the switchs inbe dam; 1 t e woflwi J e Q. c. is; at

wn ti cisune i w 1 transmissionon subscribers loops comprising, transmitting irorn the several subscribers 'stationsto the centralljofllce at 'voice frequenc!- translating. from. voice frequency to carrienireyret L i -ce tra 59m, and r n mlt ina at said severalsubscribers'stationse i 2.--'lhe combination ota subscriber: station capableiot'transmitting at voice trequency and I including a detector-"tor receivingcarrier a r r trs e r. o e cen ra mcetwee.

quency waves and converting them to voice frequencies, and a bilateral cord circuit for interconnecting subscribers lines and comprising means to translate voice frequency waves from either of two-lines to carrier irequency waves ior transmission to the opposite line;

q 31 A subscribers station comprising a transmitting branch including a transmitter and a voice filter, and a receiving branch including a :filtr for passing modulated carrier waves, a detectorand areceiver a two-wire line from said subscriberfsstationjtoa central ofllce, and a dour-Iwire cord; circuit connectible between said line and other similar lines individually and comprising ineach' side a voice filter, a modulator fortranslating voice waves to modulated carrier waves', and a carrier frequency filter, in the order named, the opposite sides of said four-wire cord circuitktr'ansmitting in opposite directions;

'4; The? combination with subscribers lines comprising 1 subscribers 1 stations each capable of transmittingvoice frequency waves and receiving and detecting carrieritrequency waves, 01 a cord circuit includinga modulator connectible-to saidalines,iwhereby incomlng voice waves from a connected' line are converted into modulated nectediline.

carrierswaves for transmission to anotherucon- 5 A telephone system comprising-a central station and lines: radiating therefrom, asource of carrier: waves and modulating means located only .atsaid central statiommeans tor-transmittingispeech we, each of said linesztosaid central station atlvolce' irequencieaEand means ineluding source of carrier waves and c said moduiatingumeans for transmitting, ir'omflsaid centralustation over any ot rsaid lines carrier waves modulated by the ;voice waves received over anotherline; u 6, The combination with subscribers lines comprising subscribers stations "capable oitrans mitting atvoicefrequencies and r. receivingfland T detecting lvoice-modulated carrier'waves, of a cord circuit connectible to said'lines comprising -a source'ot carrier waves,-a modulator. and-a illters,-,one passing speech currents and said-word circuit .whereby voice waves received overgeither, 0! (two connected lines are converted the'other line.

to modulated carrier waves for tron to ithepther carrier-waves, con- ,nected between said modulator and the endsot 

